This invention relates generally to high performance mufflers and more particularly to a muffler insert assembly for an exhaust system of an internal combustion engine, in particular a motorcycle engine.
While most mufflers used on passenger cars and light trucks are not serviceable items, that is they are not designed to be refurbished after a period of use, high performance mufflers and especially high performance mufflers for motor cycles, such as racing motor cycles are made from durable components that hold renewable sound absorbing materials that can be replaced after a period of use. Typically, a high performance racing motor cycle muffler includes a housing such as a generally cylindrical or other tubular housing. An exhaust pipe extends from the engine through the housing and terminates at an exhaust port, forming a generally co-axial structure with the housing. The portion of the exhaust pipe within the housing is a perforated core. A sound absorbing material or a series of baffles is disposed between the core and the housing to reduce engine noise. Fiberglass batting is well suited to this application and is commonly used.
After a period of use, the fiberglass sound absorbing material in a high performance muffler becomes compressed and loses its effectiveness. This both increases the noise created by the engine, and changes the operating characteristics of the engine due to changes in back pressure and the like. Because the housing and the core are more durable and have a longer lifetime than the fiberglass sound absorbing material, it is desirable to rebuild mufflers of the type just described by replacing the sound absorbing material. While the methods used for manufacturing new mufflers could theoretically be used to replace the sound absorbing material in a used muffler, such methods normally employ special tools that are either too expensive and/or not generally available for performing occasional rebuilds.
A number of methods for rebuilding mufflers have been proposed. Releasing porous sound absorbing material from a container into the muffler is one such method. This method has a number of disadvantages including inaccurate control over the amount of the material inserted, and the non-uniformity of filling. In addition, such materials have a short life. German Patent No. DE G 89 10 785 discloses a cylindrical muffler insert element made from an inner and an outer screen pipe with a filled in intermediate space. This is expensive to produce, transport, store and assemble. In addition, the insert seats imprecisely in the muffler, which is another disadvantage.
More recently, a composite insert shaped in the form of a hose has been proposed. The shaped composite can be formed by sewing strips formed of flat materials into which sound absorbing material can be inserted, and the covering sewn together. This construction is an advantage over some of the other known constructions, but has its own disadvantages. Specifically, unless the inner covering is quite durable, it may catch on the perforations in the core of the muffler during installation, and allow the sound absorbing material to shift undesirably.
In prior art which is the subject of a U.S. patent application (serial number unknown), muffler inserts are described which are formed from a predetermined amount of loosely bundled individual elements of a sound absorbing material, the loose bundle being confined roughly in an assembly shaping unit intended for insertion in the muffler. The loose bundle is fixed corresponding to the assembly shaping unit to a shape composite such that the fixed shape can be handled without individual elements loosening until assembly for the specific uses of the muffler insert. However, during the specified uses of the muffler insert the filling is at least partially released. Advantageously, the insert is released by the action of high temperature in the muffler. These can lead to the release of adhesive bonds, seams or the like and thus cause the at least partial release of the shaped composite.
It is an object of this invention to provide a muffler insert for replacing fiberglass or otherwise compressible sound absorbing material that allows the material to expand within the muffler without the need for heating the muffler to release a seal.
It is another object of this invention to provide a muffler insert that has sufficient stiffness prior to insertion that it is easy to package and ship.
Is another object of this invention to provide a method for refilling a muffler including at least the steps of compressing a sound absorbing material to form a muffler insert, inserting the insert into a muffler to be rebuilt and at least partly uncompressing the material without the need for the application of heat.
Briefly stated and in accordance with a presently preferred embodiment of the invention, a muffler insert assembly for a motor vehicle exhaust of the type including a perforated core, a housing generally coaxial with the core and a layer of tufted sound absorbing material disposed between the core and the housing includes a rigid hollow inner tube with inner dimensions exceeding the outside dimensions of the perforated core, a flexible retaining layer wrapped around the inner tube and slidably retained thereon, a flexible outer wrap overlying the retaining layer and stitched thereto around the border thereof to form a fillable space there between, and a fibrous filling compressed in the fillable space so that the inner tube can be translated along the pipe until it passes into a muffler casing and removed, releasing the fibrous filling to expand into the space previously occupied by the inner tube.
A method of refilling a muffler of the type that includes a housing and a perforated muffler core within the housing includes the steps of providing a rigid inner tube having an inside diameter greater than an outside diameter of the muffler core, forming a muffler insert having a layer of compressed sound absorbing material around the inner tube, sliding the inner tube and the layer of compressed sound absorbing material over the muffler core and removing the rigid insert core and allowing the compressed sound absorbing material to expand against the muffler core.